The Institute of Electrical and Electronics Engineers (IEEE) 802.11e specification, approved in September of 2005, defines a set of Quality of Service (QoS) enhancements for local area network (LAN), and in particular wireless LAN (WLAN), applications. For example, a QoS capability in a network may assign access categories (ACs) to various streams of packets. The assigned AC of a stream of packets may depend on the packets' priority, for example, as assigned by an application, and may be referred to as a user priority (UP). An AC may include, for example, a common set of enhanced distributed channel access (EDCA) parameters that may be used by a QoS function to contend for a channel in order to transmit packets with certain priorities. For example, the Wi-Fi Multimedia (WMM certification, which is based on the IEEE 802.11e standard, prioritizes traffic according to four access categories (ACs): voice (AC_VO), video (AC_VI), best effort (AC_BE), and background (AC_BE). Additional information regarding the IEEE 802.11e standard may be found in “IEEE 802.11e Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Amendment 8: Medium Access Control (MAC) Quality of Service Enhancements” (published 2005).
Different ACs may be associated with different power saving parameters. One such power saving parameter may be, for example, the delivery mechanism used by an access point (AP) to deliver packets to a station (STA) that is operating in a reduced power mode. For example, one delivery mechanism may be the “legacy” power save mechanism of the IEEE 802.11 standard: “ANSI/IEEE Std. 802.11, Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications” (published 1999; reaffirmed June 2003). Another delivery mechanism may be the automatic power save delivery (APSD) mechanism, e.g., unscheduled APSD (UAPSD) or scheduled APSD (S-APSD), as defined in 802.11e. A QoS station (QSTA) may define all or some of the ACs as trigger-enabled and/or delivery-enabled. A trigger- and delivery-enabled AC may use UAPSD as the default delivery mechanism, whereas an AC that is neither trigger- nor delivery-enabled may use the “legacy” power save delivery mechanism.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.